Rob appeared on the first season of Australian Idol, he also played Neighbours' former villain Finn Kelly.
And whether or not Leon had guessed his identity, it seemed that viewers of the show agreed the Wolf was Rob, with many taking to Twitter to voice their predictions.
"Rob Mills is the Wolf - this was his album title," said one viewer on Twitter.
"Millsy!! That's an easy one," tweeted another.
Even ex Bachelorette Georgia Love played along at home.
"Oh Millsy, I listened to your CD enough in 2003 to recognise your voice anyway boo #MaskedSingerAU." she tweeted.
Viewers were also left puzzled after Monday night's premiere episode around whether the stars are actually singing live.
While the official stance from Channel 10 is that the artists behind the costumes are singing live, fans aren’t entirely convinced, and took to Twitter to speak out.
“So im confused - how is this live?” wrote one user, followed by another, who said, “Hey #MaskedSingerAU, why give mics when they're masked, they're surely not singing live then?!”
Others were more disgruntled at the possibility of The Masked Singer being a farce.
“Everyone knows that no one in singing live on this sh*t right? Literally the worst show on TV,” said one user.
However, judge Jackie O Henderson is adamant that they are singing live.
“I’ve seen a set malfunction happen and something fell on one of the singers and the singing stopped straight away,” Jackie told The Advertiser. “They are singing live – 100 per cent fact.”